The invention relates to a Coriolis flowmeter and further relates to a density meter utilizing the Coriolis flowmeter.
The Coriolis flowmeter is know as a direct mass flowmeter which is designed to work under the known principle that when a tube through which a fluid to be measured flows is vibrated, a Coriolis force which is proportional to the mass flow rate is generated to give a certain effect to the movement of vibrating fluid. Generally, the Coriolis force is detected in terms of an elastic deformation or distortion of the tube.
Since the Coriolis force is small as compared with the applied vibration force, it is required to provide a force measurement system to accurately detect the generated Coriolis force with high sensitivity. Therefore, a representative Coriolis flowmeter is designed to have a U-shaped conduit so that an enlarged deformation can be detected. However, the U-shaped conduit has a disadvantageous feature in that the fluid flowing through the U-shaped tube is apt to undergo a pressure loss. Nevertheless, Coriolis flowmeters having U-shaped tube have been widely employed because they have high sensitivity when they are appropriately designed.
U.S. Pat. Nos. 4,192,184 and 4,311,054 describe a Coriolis flowmeter having two U-shaped flow loops, a vibrator, and a sensor.
Japanese Patent Provisional Publication 59-92314 (corresponding to U.S. Ser. No. 439,035) illustrates a Coriolis flow meter such as that illustrated in FIG. 6, which has a manifold a two U-shaped tubes through each of which a fluid to be measured in connection with its flow rate flows in parallel.
The Coriolis flowmeter is vibrated by the vibration generator in the primary flexural vibration in which the nodes are placed on the support blocks at both ends of the flow tube. The Coriolis force FC is expressed as follows:
Fc=xe2x88x922m[xcfx89]xc3x97[v]
[in which, [xcfx89] is a vector of xcfx89 (frequency) and [v] is a vector of v (flow rate)].
The present inventor has discovered that the conventional Coriolis flowmeter having plural flow tube type cannot show enough sensitivity.
It is an object of the invention to provide a mass flowmeter of curved tube type utilizing the Coriolis force which is improved in its sensitivity.
It is another object of the invention to provide a density meter utilizing the improved Coriolis flowmeter.
The present invention resides in a Coriolis flowmeter comprising:
a substrate having a pair of conduits through which a fluid to be measured in connection with a flow rate thereof flows;
a curved tube fixed to the substrate in such manner that one end connects with one of the conduits and another end connects with another of the conduits;
a pair of curved rods having a curve identical to the curve of the curved tube each of which is fixed to the substrate on each side in parallel with the curved tube with a space;
vibration generating meant attached to the curved tube and each of the curved rods which generate vibrations in such manner that the curved tube and the curved rods vibrate in opposite phase; and
a sensor means detecting variation of vibration of the curved tube which is caused by a Coriolis force occurring when a fluid flows through the curved tube.
The invention further resides in a Coriolis flowmeter comprising:
a substrate having a pair of colts through which a fluid to be measured in connection with a flow rate thereof flows;
a first curved tube, a second curved tube, and a third curved tube all of which are fixed to the substrate in parallel to each other in such manner that one end of the first tube connects with one of the conduits, another end of the first tube connects with one end of the second tube through a conduit arranged in or under the substrate, another end of the second tube connects with one end of the third tube through a conduit arranged in or under the substrate, and another end of the third tube connects with another of the conduits under the condition that the fluid flows in the three curved tube a direction identical to each other;
vibration generating means attached to the curved tubes which generate vibrations in such manner that the neighboring tubes vibrate in opposite phase; and
a sensor means detecting variation of vibration of the second tube which is caused by a Coriolis force occurring when a fluid flows through the curved tube.
The Coriolis flowmeter of the invention can also be utilized as a density meter.